Various rubber adhesives, particularly chloroprene adhesives comprising as a base rubber a chloroprene rubber, are utilized in various fields. There is known a one-pack chloroprene adhesive comprising a chloroprene rubber, a tackifier, and optionally a vulcanizing agent or a vulcanizing accelerator which are dissolved in an appropriate organic solvent. However, the known adhesive has inferior heat resistance, particularly less strength or creep properties at a high temperature (80.degree.-130.degree. C.), and hence, it is usually used in the form of a two-pack type of adhesive. That is, the chloroprene adhesive is used in combination with a polyisocyanate curing agent.
The present inventors had intensively studied as to an improved one-pack chloroprene adhesive which can exhibit the same or more excellent adhesion with high heat resistance than the two-pack type of chloroprene adhesive, and had found that when the chloroprene rubber is modified with an aminosilane or isocyanate silane, the rubber can exhibit excellent strength and creep properties even at a high temperature. This is because the silane promotes a crosslinking reaction in the presence of moisture once applied. U.S. patent application Ser. No. 058,849was filed on Jun. 5, 1987 which was re-filed as a Continuation-in-part application on Mar.14, 1989. However, it has now been found that when the chloroprene rubber modified with an aminosilane is incorporated with a phenolic tackifier resin (e.g. alkylphenol resins, terpene-modified phenol resins, etc.) as disclosed in said U.S. patent application, the composition still shows deterioration in properties by heating and less heat aging resistance. The present inventors have further studied to find a more improved one-pack chloroprene adhesive without using phenolic resin which induces the deterioration of properties by heating, and have now found that when a petroleum resin is used as the tackifier resin, the adhesive composition shows more improved heat aging resistance.